First Isolation of a Hybrid Shigatoxigenic and Enterotoxigenic Escherichia coli Strain Harboring the stx2 and elt Genes in Korea

Pathogenic Factors and Recent Study on the Rapid Detection of Shiga Toxin-Producing Escherichia coli (STEC)

This comprehensive review delves into the pathogenicity and detection of Shiga Toxin-Producing Escherichia coli (STEC), shedding light on its various genetic and clinical manifestations. STEC originating from E. coli acquires pathogenicity through mobility and genetic elements. The pathogenicity of STEC is explored in terms of clinical progression, complications, and key toxins such as Shiga toxin (Stx). Stx1 and Stx2 are two distinct Stx types exhibiting different toxicities, with Stx2 often associated with severe diseases. This review also delves into Subtilase cytotoxin, an additional cytotoxin produced by some STEC strains. Pathogenic mechanisms of STEC, such as attaching and effacing intestinal lesions, are discussed, with a focus on roles of genetic factors. Plasmids in STEC can confer unique pathogenicity. Hybridization with other pathogenic E. coli can create more lethal pathogens. This review covers a range of detection methods, ranging from DNA amplification to antigen detection techniques, emphasizing the need for innovative approaches to improve the sensitivity and speed of STEC diagnosis. In conclusion, understanding diverse aspects of STEC pathogenicity and exploring enhanced diagnostic methods are critical to addressing this foodborne pathogen effectively. Pathology of Shiga toxin toxicity. STEC-derived Shiga toxin consists of one A subunit and five B subunits. Pathological symptoms of the disease can progress to HUS within two weeks after the onset of diarrhea. Shiga toxin intoxication is also associated with many complications, such as neurological and cardiac complications. This figure was reconstructed based on data from Bruyand et al.

ArcA positively regulates the expression of virulence genes and contributes to virulence of porcine Shiga toxin-producing enterotoxigenic Escherichia coli

IMPORTANCE

Enterotoxigenic Escherichia coli (ETEC) cause severe diarrhea in humans and animals, leading to death and huge economic loss worldwide. Thus, elucidation of ETEC's pathogenic mechanisms will provide powerful data for the discovery of drugs serving as prevention or therapeutics against ETEC-caused diarrheal diseases. Here, we report that ArcA plays an essential role in the pathogenicity and virulence regulation in ETEC by positively regulating the expression of several key virulence factors including F18 fimbriae, heat-labile and heat-stable toxins, Shiga toxin 2e, and hemolysin, under microaerobic conditions and in vivo. Moreover, we found that positive regulation of several virulence genes by ArcA requires a global repressor H-NS (histone-like nucleoid structuring), implying that ArcA may exert positive effects by antagonizing H-NS. Collectively, our data established a key role for ArcA in the pathogenicity of porcine ETEC and ETEC strains isolated from human infections. Moreover, our work reveals another layer of regulation in relation to oxygen control of virulence factors in ETEC.

Genome-Based Characterization of Hybrid Shiga Toxin-Producing and Enterotoxigenic Escherichia coli (STEC/ETEC) Strains Isolated in South Korea, 2016-2020

The global emergence of hybrid diarrheagenic E. coli strains incorporating genetic markers from different pathotypes is a public health concern. Hybrids of Shiga toxin-producing and enterotoxigenic E. coli (STEC/ETEC) are associated with diarrhea and hemolytic uremic syndrome (HUS) in humans. In this study, we identified and characterized STEC/ETEC hybrid strains isolated from livestock feces (cattle and pigs) and animal food sources (beef, pork, and meat patties) in South Korea between 2016 and 2020. The strains were positive for genes from STEC and ETEC, such as stx (encodes Shiga toxins, Stxs) and est (encodes heat-stable enterotoxins, ST), respectively. The strains belong to diverse serogroups (O100, O168, O8, O155, O2, O141, O148, and O174) and sequence types (ST446, ST1021, ST21, ST74, ST785, ST670, ST1780, ST1782, ST10, and ST726). Genome-wide phylogenetic analysis revealed that these hybrids were closely related to certain ETEC and STEC strains, implying the potential acquisition of Stx-phage and/or ETEC virulence genes during the emergence of STEC/ETEC hybrids. Particularly, STEC/ETEC strains isolated from livestock feces and animal source foods mostly exhibited close relatedness with ETEC strains. These findings allow further exploration of the pathogenicity and virulence of STEC/ETEC hybrid strains and may serve as a data source for future comparative studies in evolutionary biology.

Prevalence, Antimicrobial Resistance, and Whole Genome Sequencing Analysis of Shiga Toxin-Producing Escherichia coli (STEC) and Enteropathogenic Escherichia coli (EPEC) from Imported Foods in China during 2015–2021

Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic Escherichia coli (EPEC) are foodborne pathogens that cause hemolytic uremic syndrome and fatal infant diarrhea, respectively, but the characterization of these bacteria from imported food in China are unknown. A total of 1577 food samples from various countries during 2015–2021 were screened for STEC and EPEC, and the obtained isolates were tested for antimicrobial resistance and whole genome sequencing analysis was performed. The prevalence of STEC and EPEC was 1.01% (16/1577) and 0.51% (8/1577), respectively. Antimicrobial resistances to tetracycline (8%), chloramphenicol (8%), ampicillin (4%), ceftazidime (4%), cefotaxime (4%), and trimethoprim-sulfamethoxazole (4%) were observed. The antimicrobial resistance phenotypes corresponded with genotypes for most strains, and some resistance genes were related to mobile genetic elements. All 16 STEC isolates were eae negative, two solely contained stx1 (stx1a or stx1c), 12 merely carried stx2 (stx2a, stx2d, or stx2e), and two had both stx1 and stx2 (stx1c + stx2b, stx1a + stx2a + stx2c). Although they were eae negative, several STEC isolates carried other adherence factors, such as iha (5/16), sab (1/16), and lpfA (8/16), and belonged to serotypes (O130:H11, O8:H19, and O100:H30) or STs (ST297, ST360), which have caused human infections. All the eight EPEC isolates were atypical EPEC; six serotypes and seven STs were found, and clinically relevant EPEC serotypes O26:H11, O103:H2, and O145:H28 were identified. Two STEC/ETEC (enterotoxigenic E. coli) hybrids and one EPEC/ETEC hybrid were observed, since they harbored sta1 and/or stb. The results revealed that food can act as a reservoir of STEC/EPEC with pathogenic potential, and had the potential ability to transfer antibiotic resistance and virulence genes.

The prevalence and genomic context of Shiga toxin 2a genes in E. coli found in cattle

Shiga toxin-producing Escherichia coli (STEC) that cause severe disease predominantly carry the toxin gene variant stx2a. However, the role of Shiga toxin in the ruminant reservoirs of this zoonotic pathogen is poorly understood and strains that cause severe disease in humans (HUSEC) likely constitute a small and atypical subset of the overall STEC flora. The aim of this study was to investigate the presence of stx2a in samples from cattle and to isolate and characterize stx2a-positive E. coli. In nationwide surveys in Sweden and Norway samples were collected from individual cattle or from cattle herds, respectively. Samples were tested for Shiga toxin genes by real-time PCR and amplicon sequencing and stx2a-positive isolates were whole genome sequenced. Among faecal samples from Sweden, stx1 was detected in 37%, stx2 in 53% and stx2a in 5% and in skin (ear) samples in 64%, 79% and 2% respectively. In Norway, 79% of the herds were positive for stx1, 93% for stx2 and 17% for stx2a. Based on amplicon sequencing the most common stx2 types in samples from Swedish cattle were stx2a and stx2d. Multilocus sequence typing (MLST) of 39 stx2a-positive isolates collected from both countries revealed substantial diversity with 19 different sequence types. Only a few classical LEE-positive strains similar to HUSEC were found among the stx2a-positive isolates, notably a single O121:H19 and an O26:H11. Lineages known to include LEE-negative HUSEC were also recovered including, such as O113:H21 (sequence type ST-223), O130:H11 (ST-297), and O101:H33 (ST-330). We conclude that E. coli encoding stx2a in cattle are ranging from strains similar to HUSEC to unknown STEC variants. Comparison of isolates from human HUS cases to related STEC from the ruminant reservoirs can help identify combinations of virulence attributes necessary to cause HUS, as well as provide a better understanding of the routes of infection for rare and emerging pathogenic STEC.

Captive Green Iguana Carries Diarrheagenic Escherichia coli Pathotypes

The green iguana appears to be a carrier for bacteria causing gastrointestinal infections in humans. The presence of diarrheagenic E. coli (DEC) pathotypes, however, has not been studied in this reptile. The aim of the current work was to investigate the prevalence of DEC in the intestines of 240 captive green iguanas, their phylogenetic groups, and the antibiotic susceptibility profile. E. coli strains were isolated from 41.7% (N = 100/240) of the intestinal content of green iguanas. DEC strains was identified in 25.9% of the screened population and were detected in the majority (62%, p = 0.009) of those reptiles carrying E. coli strains. Among DEC strains, STEC strains carrying the stx1 gene were the most prevalent pathotype isolated (38.7%), followed by EAEC and ETEC (27.4% each). Genetic markers of DEC strains belonging to the EHEC pathotype were not detected. More than a half of DEC strains were classified into the Clade I-II phylogroup (64.5%), followed by the phylogroup A (14.5%). The antibiotic susceptibility method demonstrated that a high proportion of DEC strains were resistance, or non-susceptible, to carbenicillin, amikacin, and ampicillin. We conclude that the green iguana kept in captivity is a carrier of DEC strains bearing resistance to first-line antibiotics, including penicillins. Given the increase presence of the green iguana in Latin American households, these reptiles represent a potential source of transmission to susceptible humans and therefore a potential source of gastrointestinal disease.

Molecular Characterization and Comparative Genomics of Clinical Hybrid Shiga Toxin-Producing and Enterotoxigenic Escherichia coli (STEC/ETEC) Strains in Sweden

Hybrid E. coli pathotypes are representing emerging public health threats with enhanced virulence from different pathotypes. Hybrids of Shiga toxin-producing and enterotoxigenic E. coli (STEC/ETEC) have been reported to be associated with diarrheal disease and hemolytic uremic syndrome (HUS) in humans. Here, we identified and characterized four clinical STEC/ETEC hybrids from diarrheal patients with or without fever or abdominal pain and healthy contact in Sweden. Rare stx2 subtypes were present in STEC/ETEC hybrids. Stx2 production was detectable in stx2a and stx2e containing strains. Different copies of ETEC virulence marker, sta gene, were found in two hybrids. Three sta subtypes, namely, sta1, sta4 and sta5 were designated, with sta4 being predominant. The hybrids represented diverse and rare serotypes (O15:H16, O187:H28, O100:H30, and O136:H12). Genome-wide phylogeny revealed that these hybrids exhibited close relatedness with certain ETEC, STEC/ETEC hybrid and commensal E. coli strains, implying the potential acquisition of Stx-phages or/and ETEC virulence genes in the emergence of STEC/ETEC hybrids. Given the emergence and public health significance of hybrid pathotypes, a broader range of virulence markers should be considered in the E. coli pathotypes diagnostics, and targeted follow up of cases is suggested to better understand the hybrid infection.

Hazard Identification and Characterization: Criteria for Categorizing Shiga Toxin-Producing Escherichia coli on a Risk Basis†

Shiga toxin-producing Escherichia coli (STEC) comprise a large, highly diverse group of strains. Since the emergence of STEC serotype O157:H7 as an important foodborne pathogen, serotype data have been used for identifying STEC strains, and this use continued as other serotypes were implicated in human infections. An estimated 470 STEC serotypes have been identified, which can produce one or more of the 12 known Shiga toxin (Stx) subtypes. The number of STEC serotypes that cause human illness varies but is probably higher than 100. However, many STEC virulence genes are mobile and can be lost or transferred to other bacteria; therefore, STEC strains that have the same serotype may not carry the same virulence genes or pose the same risk. Although serotype information is useful in outbreak investigations and surveillance studies, it is not a reliable means of assessing the human health risk posed by a particular STEC serotype. To contribute to the development of a set of criteria that would more reliably support hazard identification, this review considered each of the factors contributing to a negative human health outcome: mild diarrhea, bloody diarrhea, and hemolytic uremic syndrome (HUS). STEC pathogenesis involves entry into the human gut (often via ingestion), attachment to the intestinal epithelial cells, and elaboration of Stx. Production of Stx, which disrupts normal cellular functions and causes cell damage, alone without adherence of bacterial cells to gut epithelial cells is insufficient to cause severe illness. The principal adherence factor in STEC is the intimin protein coded by the eae gene. The aggregative adherence fimbriae adhesins regulated by the aggR gene of enteroaggregative E. coli strains are also effective adherence factors. The stx_2a gene is most often present in locus of enterocyte effacement ( eae)-positive STEC strains and has consistently been associated with HUS. The stx_2a gene has also been found in eae-negative, aggR-positive STEC that have caused HUS. HUS cases where other stx gene subtypes were identified indicate that other factors such as host susceptibility and the genetic cocktail of virulence genes in individual isolates may affect their association with severe diseases.